The present invention relates to a device which optically detects the coordinates of a specified position, thereby it can be used to draw images, write text on electronic boards or the like. More particularly, this invention relates to a device in which a probe beam is emitted towards a reflecting member, probe beam reflected from the reflecting member are received, and the coordinates of the specified position is detected based on the intensity of the received light.
As a conventional device which optically detects the coordinates of a specified position and inputs the detected coordinates to some other device (hereafter referred to as coordinate-position input device), there is one comprising a light emitter that emits a probe beam (irradiation light), a reflector that reflects the probe beam emitted by the light emitter, and a light receiver that receives and converges the probe beam reflected by the reflector. The radiated light is a flux of collimated light beam which is parallel but at a certain height from a coordinate input surface (a whiteboard or a blackboard).
FIG. 9 schematically shows the conventional coordinate-position input device 200. FIG. 10 schematically shows the light receiver when viewed from the vertical direction with respect to the coordinate input surface 202. A light reception/emission section 203 is provided in this coordinate-position input device 200. This light reception/emission section 203 comprises a light emitter that emits irradiation light (probe beam) along the coordinate input surface 202, and a light receiver 220 that receives the reflected light. The light emitter is not specifically shown in these figures. A recursive reflector 204 is provided on the three sides of the coordinate input surface 202. This recursive reflector 204 comprises a reflection plate that reflects an incoming probe beam recursively to the direction from which light came in. The light emitter comprises a light-emitting element that emits irradiation light, and a cylindrical lens that converges or diffuses the irradiation light emitted by the light-emitting element in a prescribed direction of its travel. The functions of this light emitter will be explained in detail later. The light receiver 220 comprises a light receiving lens 221 that receives and converges the reflection light, and a photoreceptor 222 that detects the intensity of the received light converged by the light receiving lens 221. When a position on the coordinate input surface 202 is specified by pointing that position with a pointing tool, the coordinate-position input device 200 detects the specified position in terms of its coordinates. The specified position is detected base on detection of the direction xcex8 in which the light is blocked due to the invasion of the pointing tool in the light flux. By the way, the pointing tool may be a pen, finger or the like.
Structure of the light emitter will now be explained in detail here. FIG. 11A shows the conventional light emitter when viewed from the direction parallel to the coordinate input surface 202 and also from the direction perpendicular to the direction of travel of the irradiation light. In this light emitter, a positional relation between the light-emitting element 211 and the cylindrical lens 212 is so adjusted that the irradiation light travels parallel to the coordinate input surface 202. Precisely, the light-emitting element 211 is disposed at one focal point of the cylindrical lens 212. In other words, the light-emitting element 211 is so positioned that the light coming out of the cylindrical lens 212 is parallel to the optical axis of the light emitted from the light-emitting element 211. The reason why the light-emitting element 211 is positioned in this manner is as follows. That is, by positioning the light-emitting element 211 in this manner, if the collimated light beam is blocked by the pointing tool at some place, then the shadow of the pointing tool proceeds as it is without changing its shape because of the property of the collimated light beam. In other words, a sharp shadow of the pointing took fall on the photoreceptor. Conventionally, as shown in FIG. 11B, it was considered that, because the shadow of the pointing tool is sharp it appears as a dark spot on the photoreceptor, whereby the position of the pointing tool can be detected with highest precision.
On the other hand, in another conventional method, the cylindrical lens 212 and the light-emitting element 211 are so adjusted that the light coming out of the cylindrical lens 212 is not parallel but becomes narrower (that, is the light converges) as it reaches the recursive reflector 204 as shown in FIG. 12A. This method will be called as the method of converging the light to differentiate it from the above-explained method of parallel light. When the light is converging, since the irradiation light is not collimated light, due to diffraction or the like, the shadow of the pointing tool is not sharp. Accordingly, as shown in FIG. 12B, the negative peak of the intensity of the, corresponding to the position of the pointing tool is not very distinct, furthermore, the peak is not sharp. Because of these facts the precision in detection of the position of the pointing tool degrades.
An experiment was conducted as follows. FIG. 13A to FIG. 13B show detection characteristics of the coordinate-position input device observed in this experiment. The distance between the pointing tool and the coordinate input surface is plotted along the horizontal axis. The degree of detection precision (sensitivity of the photoreceptor) is plotted along the vertical axis. The lower the value of this degree of detection precision, the higher is the precision. The method of converging light explained with respect to FIG. 12A was employed in this experiment. Further, two pointing tools, one with a diameter of 5 mm and the other with a diameter of 20 mm were used to specify a position. FIG. 13A shows the detection characteristics when the direction 0 of the pointing tool is zero degree. FIG. 13B shows the detection characteristics when the direction xcex8 of the pointing tool is 20 degrees. Finally, FIG. 13C shows the detection characteristics when the direction xcex8 of the pointing tool is 40 degrees. Each line in these plots shows the detection characteristics corresponding to the distance between the pointing tool and the light receiving lens 221. FIG. 14A to FIG. 14C correspond to FIG. 13A to FIG. 13C with the difference that the method of parallel light explained with respect to FIG. 11A was employed.
When the method of parallel light is employed, it is clear from FIG. 14A to FIG. 14C that, the precision of detection of the specified position increases as the distance between the pointing tool and the coordinate input surface decreases. Further, it is apparent that, the distance between the pointing tool and the light receiving lens 221, the direction xcex8, or the size of the pointing tool does not make any difference. In other words, if the method of parallel light is employed in the coordinate-position input device, then the specified position can be detected at a high precision. Furthermore, the detection characteristics depend only on the distance between the pointing tool and the coordinate input surface and does not depend on any other parameter.
On the contrary, when the method of converging light is employed, it is clear from FIG. 13A to FIG. 13C that, the detection precision is not uniform because it is affected by the distance between the pointing tool and the light receiving lens 221, the direction xcex8, or the size of the pointing tool. Particularly, the detection precision is low even if the pointing tool is brought very close (of the order of 1.0 mm) to the coordinate input surface.
As can be seen from the results of the experiments, the detection precision in the conventional coordinate-position input device is improved by employing the method of parallel light.
However, the conventional method has following problems. Consider that a whiteboard is used as a coordinate input surface, and some image is actually drawn with a pointing tool (for example, a pen) on the coordinate input surface. It is important that the precision in detection of the specified position is high when the pointing tool is touching the coordinate input surface. In other words, whether the coordinate-position input device is good or bad is determined in many cases according to how high the detection precision of input coordinates on the coordinate input surface is. However, as can be seen from FIG. 13A to FIG. 14C, the precession in detection of the specified position in the conventional coordinate-position input device is quite low when the distance between the pointing tool and the coordinate input surface is zero. Thus, there was a requirement of a coordinate-position input device with still higher detection precision as compared to the conventional one.
It is an object of this invention to provide a coordinate-position input device with improved precision in detection of a coordinate input position.
According to the coordinate-position input device of one aspect of this invention, the probe beam spreads along the coordinate input surface rather than being parallel or converging. Thus, when viewed from the side of the light receiver, the light is focused on it because the light is recursively reflected by the recursive reflector. Accordingly, precision in detection of a specified position when the pointing tool touches the coordinate input surface is improved.
According to the coordinate-position input device of another aspect of this invention, the coordinate-position input device has a light-emitting element that emits a probe beam to detect a coordinate input position and a refractive lens that refracts the probe beam emitted by the light-emitting element to be a beam flux to travel in a prescribed direction. Further, the light-emitting element is disposed at a location closer to the refractive lens than the focal point of the refractive lens. Thus, when viewed from the side of the light receiver, the light is focused on it because the light is recursively reflected by the recursive reflector. Accordingly, precision in detection of a specified position when the pointing tool touches the coordinate input surface is improved.
Other objects and features of this invention will become apparent from the following description with reference to the accompanying drawings.